1. Field of the Invention:
The present invention is generally related to a magnetic sensor and, more particularly, to a geartooth sensor in which a carrier is shaped to form a cavity within its sensing face and in which a magnetically sensitive chip is attached directly to one of a plurality of leads.
2. Description of the Prior Art:
Many different types of magnetic sensors, including geartooth sensors, are well known to those skilled in the art. U.S. Pat. No. 5,500,589, which issued to Sumcad on Mar. 19, 1996, describes a magnetic sensor with a carrier that has a cavity shaped to receive a magnet in sliding association therein. Ribs are provided to guide the movement of the magnet into the cavity and a deformable rib is used to hold the magnet at a precise position determined by an active calibration process. A magnetically sensitive component is rigidly attached to a substrate and the substrate is rigidly attached to the carrier in which the cavity is formed. Electrically conductive leads are molded into the carrier and extend through the carrier to positions where they can be electrically connected to circuit runs on the substrate A flexible wall can also be formed in the carrier to deflect in response to the insertion of a magnet into the cavity. This provides additional holding capability that retains the magnet in position when an external force is removed.
U.S. Pat. No. 5,477,143, which issued to Wu on Dec. 19, 1995, describes a proximity sensor that has two magnetoresistive elements in a common plane and displaced from a lateral surface of a permanent magnet. The common sensing plane of the magnetoresistive elements extends in a direction parallel to a magnetic axis of a permanent magnet that extends between the north and south poles of the magnetic. A detection zone is defined relative to a preselected magnetic pole face and the magnetoresistive elements provide first and second signals that can be compared to define a third signal which is representative of the presence or absence of the magnetically permeable object within the detection zone. The magnetoresistive elements can each have a plurality of magnetoresistors which are arranged in a Wheatstone bridge configuration for the purpose of providing the first and second signals described above.
U.S. Pat. No. 5,469,055, which issued to Mueller et al on Nov. 21, 1995, discloses a dual complementary target arrangement which enables targets to be formed as an integral part of a cam shaft. The complementary target arrangement is intended to be sensed by a geartooth sensor.
U.S. Pat. No. 5,444,370, which issued to Wu on Aug. 22, 1995, describes a magnetic sensor that is provided with two target tracks arranged in generally parallel association with each other. Each of the target tracks comprises magnetic and nonmagnetic segments which are arranged in alternating patterns. Each magnetic segment of the first target track is disposed along side a nonmagnetic segment of the second target track and each magnetic segment of the second target track is disposed along a nonmagnetic segment of the first target track.
As a result of government regulations and the desire, by automobile manufactures, for the ability to provide misfire detection in automobile engines, the required accuracy and repeatability of automotive geartooth sensors have been steadily increasing in recent years. In combination with these increasing requirements, operating conditions of geartooth sensors now include increased airgap dimensions and axial runout conditions In order to properly operate with increased airgap and increased axial runout conditions, larger effective magnetic signals are required to improve the signal to noise ratio of the device. The magnitude of the effective magnetic signals in a geartooth sensor can be increased by increasing the size and strength of the permanent magnet or, alternatively, by decreasing the distance between the permanent magnet and the target. If the size and strength of the magnet are increased, the overall costs of the geartooth sensor will also be increased. A less expensive alternative method to produce larger magnetic signals is to design a packaging concept for the geartooth sensor that will minimize the distance between the permanent magnet and the ferromagnetic target. This reduction in the distance between the magnet and the target can also permit smaller permanent magnets to be used at a reduced cost.
In DC coupled geartooth sensors, mismatches and offsets of the magnetic sensing elements or components are also very important. In effect, it is the ratio of the magnetic signal to the offset magnitude of the magnetic sensing elements that is most critical to achieving high accuracy over difficult operating conditions. It would therefore be significantly beneficial if a geartooth sensor could be provided with a reduced distance between the pole face of a permanent magnet and the ultimate target, such as the ferromagnetic teeth of a gear.